It is the objective of this grant to initiate a pilot research project to study the effect of aging on the flavoprotein, NADPH-cytochrome P-450 (c) reductase. This enzyme is a very important protein that is involved in the microsomal electron transport system that metabolizes drugs, carcinogens, and steroids. It has been shown that the reductase is altered in senescent Fischer 344 rats and the loss of this enzyme in aging may help to explain the changes in drug metabolism activities and metabolite patterns in the elderly. This grant proposal will investigate the nature of the NADPH-cytochrome P-450 (c) reductase that accumulates in aged Fischer 344 rats and compare these properties with those obtained from young rats. The reductase will be purified by affinity chromatography from old and young rats and added to enzyme systems containing purified cytochrome P-450 to determine its ability to support the hydroxylation of benzphetamine. The mechanism of the inactivation of the reductase will be carefully examined to determine if a hydrogen peroxide generating system is responsible for the decrease in NADPH-cytochrome P-450 (c) reductase. Studies will be performed in vivo in young rats to increase the formation of hydrogen peroxide by the cytochrome P-450 monooxygenase to determine if this will accelerate the accumulation of the altered reductase form. In addition, similar experiments will be performed in vitro in a purified reconstituted system to determine if hydrogen peroxide will inactivate the reductase. The data obtained from this pilot project should provide us with an understanding of the biochemical mechanisms that cause cells to age and develop a rat model which can be used to monitor the aging process at a molecular level.